1. Field of Invention
This invention relates to prosthetic devices for total knee arthroplasty (TKA).
2. Discussion of Related Art
Total knee arthroplasty (TKA) is a surgical procedure for replacing a patient's injured or damaged knee joint with an artificial knee joint. TKA may be used to relieve pain caused from osteoarthritis and rheumatoid arthritis. TKA may also be performed to ameliorate discomfort resulting from deformed and unstable knees, cartilage destruction, and severe patellofemoral arthritis. As known to those of skill in the art, other indications, such as severe trauma, may also be treated with total knee arthroplasty.
Total knee replacement (TKR) has been performed in damaged and diseased knees for many years. In TKA, the posterior cruciate ligament (PCL) may either be retained or resected. If the PCL is retained, a cruciate retaining (CR) TKR prosthesis is used; if the PCL is resected, a cruciate substituting (CS) TKR prosthesis is used. The indications for using either a CR prosthesis or a CS prosthesis are known to those of skill in the art.
A knee joint prosthesis generally comprises three parts: a femoral component, a tibial component, and a patellar component. However, an individual's natural patella may continue to be used in some situations rather than replacing it with a prosthetic patellar component.
The femoral component is generally “U” shaped and implanted on the end of a patient's femur to replace the damaged surfaces of the femur while maintaining a substantial amount of the patient's natural femur. The tibial component comprises a tray, which replaces the upper surface of a patient's tibia, and a stem used to anchor the tibial tray in the patient's natural tibia. Generally, the tibial component has a metallic base with a plastic spacer on the tibial tray that provides a smooth surface to facilitate movement between the femoral component and the tibial component. The patella has a contour which tracks a portion of the femoral component during flexion and extension.
In TKA, the damaged surfaces of the knee joint are surgically removed and replaced with artificial surfaces. In particular, the ends of the femur and tibia are cut away, and prosthetic femoral and tibial components are placed over the cut ends of the respective leg bones. Due to the constant movement of the femur, tibia, and patella with respect to one another, the particular alignment of the femoral and tibial components may affect the long-term success of TKA. It has been suggested that various factors, such as geometry and alignment of the femoral component, may be associated with unbalanced collateral ligaments, lift off of the femoral component relative to the tibial component during gait, and premature loosening and subsequent failure of the implant. The geometry and alignment of the femoral component may also be associated with subluxation or inadequate movement of the patellar component relative to the femur.